The present invention relates generally to charging circuits for rechargeable batteries, and more particularly to a circuit for limiting undesirable current discharge from a battery during startup of a battery charging circuit.
Many portable electronic devices use a rechargeable battery as a power source. Example portable electronic devices include computers, cellular telephones, pagers, radios, and the like. While there are many types of rechargeable batteries used today, including nickel cadmium and nickel metal hydride, lithium ion batteries have become a popular choice. Lithium ion batteries are typically smaller and lighter than other rechargeable battery types with increased charge capacity.
The charging of lithium ion batteries is conducted in a different manner than the charging of nickel type rechargeable batteries. Generally, nickel-type rechargeable batteries are charged by applying a constant current from a battery charger to the battery until the cell reaches a predetermined voltage or temperature. A lithium ion cell, however, uses a different charging process. First, the lithium ion cell is supplied with a current from a battery charger until the cell""s voltage rises above a threshold. Next, the battery charger is held at the threshold until the current of the cell decreases to a predetermined level. Damage to at least the battery or battery charger may occur when a battery charger applies an improper voltage to a rechargeable cell.
The present invention is directed to a circuit for limiting a current that is initially discharged from a battery through a battery protection circuit. A resistive path from the battery to the detected voltage is formed when a voltage that is sufficient for charging a battery is detected. A charging signal also is provided in response to the detection of the voltage. A second path that has substantially no resistance is formed between the detected voltage and the battery when the charging signal attains a voltage that is suitable for charging the battery.
According to one aspect of the invention, a circuit for limiting a current that is initially discharged from a battery through a battery protection circuit is provided. The circuit comprises a controller, a first switch, a charging circuit, and a second switch. The controller is configured to detect the presence of a first voltage that is suitable for powering a charging circuit for the battery. The first switch is configured to couple a resistive path from the first voltage to the battery in response to the detection of the first voltage. The charging circuit is configured to provide a charging signal in response to the detection of the first voltage. The second switch is configured to couple the first voltage to the battery via a path that has substantially no resistance in response to the charging signal attaining a second voltage that is suitable for charging the battery.
According to another aspect of the invention, a method for limiting a current that is initially discharged from a battery through a battery protection circuit comprises detecting the presence of a first voltage that is suitable for powering a charging circuit for the battery. A resistive path is coupled from the first voltage to the battery in response to the detection of the first voltage. The charging circuit is enabled in response to the detection of the first voltage. The first voltage is coupled to the battery via a path that has substantially no resistance in response to a charging signal from the charging circuit attaining a second voltage that is suitable for charging the battery.
A more complete appreciation of the present invention and its improvements can be obtained by reference to the accompanying drawings, which are briefly summarized below, to the following detailed description of illustrated embodiments of the invention, and to the appended claims.